Thanks to a twentysomething Israeli tech whizz-kid based in San Francisco, the attitude of America’s tech and corporate leaders to U.S. President Donald Trump’s ban on refugees and visitors from seven Muslim countries is quite clear. They hate it.

GreatCompany.org, a website launched on Tuesday, lists nearly 200 of the biggest companies in America, including tech giants Apple, Google, Microsoft and Amazon alongside traditional names like Coca-Cola, Nike and Starbucks. Visitors can search for companies by name, see whether they support or oppose Trump’s executive order, and read statements from company executives.

The online database was created byJerusalem-born Daniel Gross, who in 2013 at age 21 sold his start-up Cue for $40 million to Apple, where he served as a director until January.

“Right now at JFK there's an Eisenstein. Or a Freud. Or a Kepler,” Gross tweeted on Saturday. “Do we really want to send their brilliance to China?” he asked the U.S. president.

Gross appealed to friends for programming help and three days later, the database went live.

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“Like some of you, we were frustrated by the recent executive action against immigration,” he wrote. “We weren't sure what to do. Then we realized we had a powerful tool in our hands: the companies we worked at.

CEOs listen to the public, and they really listen to their employees. If you speak up, your CEO might too. And if we could show the country how many business leaders opposed the recent action, perhaps we could cause it to change.”

The effect of Trump's ban on visitors from the seven affected countries was immediate. Samira Asgari, an Iranian scientist at the Ecole Polytechnique Fédérale de Lausanne, described how she was refused permission to board a flight at Frankfurt on Saturday on her way to begin a postdoctoral fellowship at a Harvard hospital to continue her research in genomics of infectious disorders.

She told the BBC she had been planning the fellowship for more than a year and even if she managed to get a visa in another 90 days, the delay would mean having to cancel a once-in-a-lifetime opportunity.

“I was pretty excited to join [the] lab but denied boarding due to my Iranian nationality. Feeling safer?” she tweeted.

Even after a U.S. court objected to President Trump’s ban, Asgari was still denied permission to fly. “Despite the Federal Court restraining order Iranians still can’t fly to Boston. Is this legal?” she asked.

Microsoft CEO Satya Nadella led his company’s charge against the ban.

“As an immigrant and as a CEO, I’ve both experienced and seen the positive impact that immigration has on our company, for the country, and for the world,” Nadella said in a message to Microsoft employees. “We will continue to advocate on this important topic.”

LinkedIn distributed a blog by Meg Garlinghouse, Yahoo! head of community affairs, stating that LinkedIn is “is committed to creating economic opportunity for all members of the global workforce, regardless of country of origin or religious belief. These are precisely the values on which our country was founded.”

She announced plans to accelerate “pre-existing plans to expand our refugee program to the U.S. to support refugees already residing in this country.”

“We are grateful to have world class talent from these recently affected countries working for us and will do everything in our power to protect their status,” she declared.

"The primary focus for our HR and legal teams is on helping the 11 LinkedIn employees that are directly impacted by the Executive Order,” a LinkedIn spokesperson told Haaretz.

“But we know that the vast majority of our employees are feeling the negative impact this is having on so many people's lives. The United States was built in large part by the work of immigrants and we believe that we should continue to support those looking to make a better life here."

Experts say the tech community is up in arms because the free flow of people and ideas has proved essential to the growth of entrepreneurship in the United States, and Trump’s order could directly harm tech development.

“Silicon Valley exports technology and imports the world’s best talent. That is how it has helped grow America’s economy and boosted its competitive advantage,” Vivek Wadhwa, a Distinguished Fellow of Carnegie Mellon University Engineering at Silicon Valley, wrote in the Washington Post.

“Immigrants are essential to our economic present and future. These newcomers start a disproportionate number of U.S. businesses, particularly in advanced technologies.

Immigrants and foreign-passport holders occupy a growing majority of places in graduate education programs in computer science, mathematics, physics and other hard sciences. They play an outsize role in U.S. research and innovation.”

A 2012 research paper that he co-authored, “America’s New Immigrant Entrepreneurs: Then and Now,” showed that 24.3 percent of U.S. engineering and technology start-up companies, and 43.9 percent of those based in Silicon Valley were founded by immigrants.

“It is no wonder that executives at almost every major technology company, including Alphabet, Facebook and Apple, have made statements defending immigrants and distancing their companies from the president. These companies are worried about their survival and the future of the country,” Wadhwa wrote.

The power of the internet was not deployed only in order to oppose Trump’s ban. Within hours of a deadly shooting attack that left six dead at a Canadian mosque on Sunday, rumors were swirling across the web that the gunmen were exactly the type of unwanted migrant targeted by Trump as terrorists in disguise.

“Just for the record the gunning down of 6 worshippers in Quebec City this week was carried out by two Syrian ‘refugees’ that arrived in Canada only last week!” a Facebook user commented on Tuesday, citing a report that she said had since “disappeared” from a Canadian newspaper’s website

Haaretz.com, the online edition of Haaretz Newspaper in Israel, and analysis from Israel and the Middle East. Haaretz.com provides extensive and in-depth coverage of Israel, the Jewish World and the Middle East, including defense, diplomacy, the Arab-Israeli conflict, the peace process, Israeli politics, Jerusalem affairs, international relations, Iran, Iraq, Syria, Lebanon, the Palestinian Authority, the West Bank and the Gaza Strip, the Israeli business world and Jewish life in Israel and the Diaspora.